This invention relates generally to multiple extension apparatus such as the telescoping booms of truck mounted cranes and similar machines. More specifically, the invention is directed to a color coding scheme which correlates the various boom stages with the corresponding sections of load charts and boom extension charts that are commonly used in connection with equipment of this type.
Truck mounted cranes are used in a variety of situations to handle various types of loads. Typically, equipment of this nature includes a multiple stage boom assembly which is mounted rotatably on a turntable with the main frame attached to the truck frame and which is also pivotal up and down about a horizontal axis. The boom stages are usually telescopically extensible and retractable by means of a hydraulic system having suitable controls. In addition, a jib which is often included may be mounted in extension from the outer boom stage in order to increase the overall length of the boom.
Loads that can be safely handled by the boom with only the intermediate boom stage extended can be excessive for the same boom angle but with the outer boom stage also extended. Similarly, a load that can be easily handled with the boom raised to a considerable angle above horizontal can be excessive if the boom is lowered such that its effective horizontal length is increased, thereby increasing the moment applied about the base end of the boom. In addition, for a given effective horizontal length of the boom, loads can be handled more safely with only the intermediate boom stage extended than with the outer stage also extended, since the strength of the smaller outer stage is less than that of the larger intermediate stage. Consequently, at each pivotal position of the boom, there is a maximum load that can be safely handled with the boom at a particular stage of extension. If attempts are made to handle loads greater than the maximum safe load, the resulting instability can cause overturning of the truck, extensive damage to the boom or other portions of the machine, and more importantly, serious injury to workmen and others.
In order to decrease the likelihood that attempts will be made to use the boom for lifting excessive loads, manufacturers commonly provide load charts which indicate the maximum load that can be safely handled at various boom positions. Also, a boom extension chart and associated pointed are usually provided on the boom glove to indicate the boom angle and the effective horizontal moment arm of the boom at various positions. If the load chart indicates that the load is excessive for a particular position of the boom, the boom must either be retracted or pivoted upwardly so as to decrease its effective horizontal moment arm before the load can be safely handled.
Even though charts of this type have been helpful, they are rather difficult to read correctly and may not completely solve the problems of personal injury and equipment damage that can occur when excessive loads are lifted. For example, even though the boom extension chart may be read properly to indicate the correct angle of the boom above horizontal, if reference is inadvertently made to the wrong section of the load chart for that angle, there may be an indication that the load can be safely handled when in fact it cannot. Therefore, despite the widespread use of load charts, unsafe conditions can still arise with considerable frequency, primarily due to human error and usually because reference could be made to an incorrect section of the load chart. It is this particular problem that the present invention is aimed at solving.
More specifically, it is an object of the invention to provide a color coding system that correlates the various stages of a telescoping boom with the corresponding sections of accompanying load and boom extension charts. The color coding scheme provided by this invention results in virtual elimination of the human error that can be involved in reading the charts and assures that reference is made to the proper sections of the chart for all positions of the boom. Consequently, the personal injury and equipment damage that has plagued this type of machinery is minimized.
Another object of the invention is to provide a color coding system which is simple and economical and which can be applied to both new and used equipment.
Yet another object of the invention is to provide a color coding system that is readily adapted for use with various types of multi-stage boom assemblies and various types of charts.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawings.